Bob was a farmer and was helping one of his cows give birth, when
 he noticed his 4-year-old son standing wide-eyed at the fence,
 taking in the whole event.
 
 "Oh great...", thought Bob, "...he's only 4 and I'm gonna have to
 start explaining the birds and bees. No need to jump the gun -
 I'll just let him ask, and I'll answer."
 
 After everything was over, Bob walked over to his son and
 asked, "Well son, do you have any questions?"
 
 "Just one." gasped the still wide-eyed lad.  "How fast was that
 calf going when he hit that cow?"